bigfish

Hello all. Just a question about the concern that everyone expresses about exhaust temps with their trucks. Is this a concern shared by tractor trailer operators as well? I understand that that EGT's become more of a concern as more power is made with more fueling through mods. But I also understand that the big trucks that are on the road are making a lot of power with high-output diesels. I have never seen or heard one of these trucks letting off the go-pedal on a hill while creeping along loaded. They appear to mash it making a lot of smoke and heat. What gives? Do these engines just de-fuel automatically if EGT's get too high?

spots

I would have to think in stock configuration that the trucks won't have EGT problems. I know I never worried (or do now) about EGT when driving big trucks. But then again I didn't own them either. Just drop gears and put it to the mat.

DieselDaze

Ive only had one truck (57 Pete) that I could get the EGT readings on. It was restored to near original configuration and its EGT's were about the same as our Dodge CTD's.
I never pushed the 57 and never had it out on any grades. Around town, I never saw its EGT's go over 700*.

However, I should also note that Im not entirely certain the gauge was working right either.

Rich

Monty

You can spec new class 8's out to have an EGT gauge and are pretty common. With the standard mounting location post turbo. Most of the time the driver actually goes by the pyro more than the speedo which is what I would want if I were a fleet owner.

wannadiesel

My work truck isn't quite a "big rig", but it's close. I put pyro and boost gauges on it because even though I don't own it, I try to drive it as though I do. The motor is set to the top rating Cat allows on a 3126 in a commercial truck - 300 HP @ 2200 RPM/860 ft. lbs. @ 1440 RPM. It's impossible to get the EGT to an unsafe level if you don't let the motor bog down. If I keep the revs over 1800, I can hold the pedal to the floor for as long as necessary to climb the hill. If I let it bog down below that, I have to watch the pyro because it will get hot after a minute or so, but no sense in downshifting when you're about to crest the hill unless it's too hot.

P Kennedy

Your CTD will work just as hard as any big truck within the confines of stock configuration and load weight specifications. You should be able to pull all day long loaded hot or cold and never have a problem. Abuse will always cause premature failure as will drag racing or extreme off roading, the Cummins is an industrial engine just like in a class 8 tractor. Unlike the Ford Powerstroke which is being used in class 4/5 chassis and the Duramax they are not built to the same standards for longevity. If you research them you will find like as every where else the inline 6 remains more consistantly reliable under high stress loading than a V8. Fuel enhancement devices require more attentiveness while pulling and can cause damage whether in a large truck or small and the gauge is your best bet for prevention after you learn and understand what it is telling you. Post turbo EGT's of 1100F+ will result in nuclear melt down,piston welding or holes from injected fuel as the aluminum melts. PK

thumper 549

your going to have stipulate which decade of truck you are feferin to- the new ones are all computer operated and will stay with in the programed confines.
In the 70s we all had egt guages and no computer just a calibrated right foot
B4 that 200 hp was all you could get out of a Big eng and temp was not a problem till we figured out how to re-button pumps shim stuff like puff limiters and blah blah.
Owner operators eventoday have egt guages but the maj fleet guys do not........they do not know what eng is under the hood ,,but that is an other story

cp

Back in the old days (anyone remember the 220, 250, 262, 270 & 335 Cummins?)it was a cardinal sin to 'lug' these engines. They had to be kept in the 1700-2100 rpm range. That is why transmissions typically had more gears then than today. Todays engines have much wider operating ranges are much more forgiving of being operated at lower rpms and full throttle than the old ones were. Cat says it's OK to run their engines below peak torque for a while. They must be right-- we had the 3406 which governed at 1800 rpm and had peak torque at 1200 and it would crest hills fine at 1000-1100. Never saw any ill effects from doing that. OTOH, an old Cummins 262 bit the dust from one lightly loaded 200 mile trip in which the 5x3 transmission was reduced to a five speed only. Blew all three head gaskets. That truck had a pyrometer in it and you could watch the egt climb but couldn't do anything about it because of the wide gear ratios when using only five speeds. The other trucks had 'poor man's pyros' on them--the convex mirror which you use to watch the top of the exhaust stack (for clearance) will show when you're into it too much--especially at night, you could sometimes see fire coming out.

I don't know what is different about the new engines (electronic controls, maybe?), but they apparently don't have the same problems.

wannadiesel

Yeah, it doesn't seem to me like it would be hard to program the engine computer in such a way that you couldn't melt the motor. They're already looking at boost pressure, RPM, air temp, and throttle position. It would be simple enough to have the computer start to cut fuel if the gas pedal is mashed and RPM is climbing too slowly or dropping, this would force even an idiot to downshift. The computer could also look at boost and air temp to see if full fuel will be potentially dangerous. They might already be doing this for all I know...

Anyway, something similar I've noticed with the Cat in my truck, if I let the motor bog a bit and then downshift on a hill, it seems to fuel harder than if I downshift before the hill and hit it at peak power. There's a hill that I used to hit at peak RPM in 7th, boost at the top would be 21 PSI. Now I hit it at about 1,800 RPM in 8th, let the motor bog back to 1,500 RPM, then shift to 7th. Speed at the top of the hill is the same, boost is 24 PSI. The only thing I can think of is that the computer is programmed to "encourage" the driver to use the highest gear possible for a given load.

cp

That is definitely true of some Cat engines. The 'multi-torque' engines will give higher torque in the top two (I think? or maybe just top one) gears.

chaikwa

Wow, no one here remembers the old mack 237 engines with the straight 5 speeds? Those were designed to be lugged, but you HAD to watch the pyrometer to make sure the temp didn't get too high. And with only 5 speeds, it was kinda easy to do too.

I was used to Cummins' with 13 speeds, and when I went to a MAck, I was always glued to that **** pyrometer! I never DID get used to lugging the engine down as much as you HAD to, to get into the next lower gear.

cp

I remember the Macks with 5 speeds. Mack learned early on how to make an engine with a wide rpm band, now everyone does it.